Since their discovery, antibiotics have become critical in the fight against infectious diseases caused by bacteria. However their extensive and inappropriate use is one of the biggest drivers of drug resistance; see. e.g., Davies, S., Infections and the Rise of Antimicrobial Resistance, Annual Report of the Chief Medical Officer—Volume Two, 2011; Chan, M., Combating Antimicrobial Resistance: Time for Action conference, WHO, 2013; and J. W. Ndieyira et al. in Nature Nanotechnology 3(11), pages 691-696, 2008.
The emergence of new infections and the re-emergence of old enemies, such as antibiotic-resistant hospital ‘superbugs’, methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-resistant Enterococci (VRE), and the associated increase in fatalities, is a major global healthcare problem, costing the NHS alone £1bn per annum. At the same time, the antibiotic-pipeline has nearly dried up with just a few new classes of antibiotics discovered over the last forty years; see e.g. M. A Cooper et al., Nature 472, page 32, 2011 and M. S. Butler et al. in Journal of Antibiotics 64(6), pages 413-425, 2011. This lack of new potent drugs puts us at risk of returning to the pre-antibiotic era of untreatable infections, or as the WHO recently forecasted “the world is heading for a post-antibiotic era”. Therefore, there is an urgent need for tools to improve the stewardship of antibiotics to minimise the evolutionary pressure on bacteria, which inevitable leads to antimicrobial drug resistance.
In clinics, the administrated drug concentrations for many drugs, including (glycopeptide) antibiotics, relies on a combination of clinical judgment, averaged pharmacokinetic models and subjective methods of assessing the effect of the therapy, resulting in an inherent variability in the quality of therapy. The administration of many therapeutic drugs, for example a glycopeptide antibiotic such as Vancomycin, is routinely guided by therapeutic drug monitoring (TDM) which can be significantly improved with more frequent monitoring, particularly in the first 24 hours of administration. Conclusively, there is an urgent need for new technologies to tailor treatments to individual patients' needs, particularly patient populations at risk, such as paediatrics, obese, elderly, immune-compromised, intensive care unit (ICU) and oncology patients.
Furthermore, in the special case of the glycopeptide antibiotic Vancomycin with its possible nephrotoxicity, patients which receiving concomitant nephrotoxic drugs are at high risks of undesirable toxic side effects. Therefore especially for those patients, there is an urgent need for monitoring drug levels at the point-of-care within minutes in order to personalise and optimise therapy at the patient level. This need has been recognized as early as 2002; see C. M. Tobin et al., Journal of Antimicrobial Chemotherapy, 50(5), pages 713-718, 2002. The British National Formulary (BNF) recommends peak serum values for Vancomycin to be in the range of 25 to 40 μg/ml which corresponds to 17.3 to 27.6 μM of Vancomycin, and trough values should be in the range of 10 to 15 μg/ml and 15 to 20 for complicated infections which corresponds to 6.9 to 10.4 μM and 10.4 to 13.8 μM Vancomycin respectively. For paediatrics the peak serum values can reach 60 μg/ml, which corresponds to 41.4 μM of Vancomycin, and trough values are typically measured in the range of 5 to 10 μg/ml which corresponds to 3.5 to 6.9 μM Vancomycin.
The state-of-the-art in clinics for therapeutic Vancomycin monitoring requires extensive sample preparation and often the samples have to be sent to a specialised laboratory with trained staff. This is expensive, laborious, time-consuming, and leads to inevitable delays between tests and results, which means important therapeutic decisions are delayed and patient pathways can be slow and cumbersome, as also recognized by M. A Cooper et al., Nature 472, page 32, 2011 and by C. M. Tobin et al., Journal of Antimicrobial Chemotherapy, 50(5), pages 713-718, 2002.
Furthermore, routine drug monitoring only measures the total antibiotic concentration even though protein binding varies dramatically (10-82% protein bound) with 55% often quoted as the mean fraction bound; see e.g. Zeitlinger et al., Antimicrobial Agents and Chemotherapy 55(7), pages 3067-3074, 2011. Since measurement of the free Vancomycin concentration requires several preparation steps and is consequently very time consuming and expensive, it is not routinely performed in health care facilities see e.g. Berthoin et al., International Journal of Antimicrobial Agents 34(6), pages 555-560, 2009. This is problematic as it is generally accepted that only the free drug fraction is pharmacologically active and the fraction of drug bound to serum proteins is inactive. Moreover, studies have suggested that the correlation between free and total fraction is poor, see e.g. Estes & Derendorf, European Journal of Medical Research, 15(12), pages 533-543, 2010 and Butterfield et al. Antimicrobial agents and Chemotherapy 55(9), pages 4277-4282 2011.
The current gold standards in therapeutic Vancomycin drug monitoring are:                fluorescence polarisation immunoassay (FPIA), such as the “FLx/TDx” from Abbott Diagnostics, UK.        homogenous enzyme immunoassay, such as the “ONLINE TDM Vancomycin assay” from COBAS®, Roche, CH.        
In 2002, NHS Bristol launched a survey to study Vancomycin therapeutic drug monitoring (TDM) as disclosed by C. M. Tobin et al., Journal of Antimicrobial Chemotherapy, 50(5), pages 713-718, 2002. They questioned 310 participants from UK NHS hospitals, UK public health laboratories, UK private hospitals and other European and non-European hospitals. According to this survey, the cost of a Vancomycin assay including taking blood, transport to the laboratory (since microbiology departments are still the main providers of assays), time for paperwork, running the assay, result reporting and interpretation was estimated to cost around £35, which exceeds the drug costs for twice-daily 1 g intravenous dosing.
Moreover the Tobin study showed that around 65% of all assays only received their results in one day. Almost exclusively, 97% of the respondent were using the fluorescence polarisation immunoassay (FPIA) purchased from Abbott Diagnostics, Maidenhead, UK.
Furthermore a recent study published by Touw et al. in European Journal of Hospital Pharmacy Science, page 13, 2007, presented the results of cost-effectiveness study of therapeutic drug monitoring (TDM). Their study published results on aminoglycoside and Vancomycin treatments and showed a statistically significant higher death rate (6.3%), longer stays in hospitals (12.3%), higher hearing loss (46.3%) and renal impairment (34.0%), and consequently higher total charges (6.3%) in hospitals that did not have pharmacist-managed therapies, which includes TDM combined with results interpretation by using mathematical and pharmacokinetic models and then advising the physicians correspondingly. Conclusively they recommend that Vancomycin therapy is guided by TDM, especially in patient populations at risk such as ICU patients, oncology patients and patient receiving concomitant nephrotoxic medicines.
It is therefore clear that there is a long-felt need for more facile and accurate detection of antibiotic levels, and in particular glycopeptide antibiotic levels in the complex sample matrix of a patient at the point of care, and in particular Vancomycin levels, to facilitate rapid TDM at the point-of-care. In particular, a need exists to accurately detect free (unbound) and bound fractions of glycopeptide antibiotics in such complex sample matrices at the patient's point of care.